A line graph is a visual representation of two sets of related data. It is the name given to a graph where the individual points are joined by a line or lines.
Example
The percentage of pupils in a school achieving level 5 in the end of key stage 3 assessments was recorded in the table below.
Percentage of pupils achieving level 5 in the end of key stage 3 assessments
| Year |
1999 |
2000 |
2001 |
2002 |
2003 |
|---|
| % of pupils achieving level 5 |
27% |
34% |
43% |
37% |
40% |
|---|
The table and the line graph represent the same data. The graph provides a visual representation of the changes in the school’s performance over a period of time, but the points relating to the years would not normally be joined up; they have been here to help to show the trend.
Worked examples
Example one
By how many percentage points did GCSE achievement of five of more (A*- C) passes increase from 1999 to 2003?
Find 1999 on the ‘year’ axis, move vertically upwards to the graph line, then horizontally across to the ‘percentage of pupils’ axis. The corresponding value is 34%.
Now do the same for 2003. The value on the ‘percentage of pupils’ axis for 2003 is 43%.
Subtract the 1999 figure from the 2003 figure to obtain the percentage point increase:
43% - 34% = 9%.
So GCSE achievement of five or more (A* – C) passes from 1999 to 2003 increased by 9 percentage points.
Example two
What is the change, between 2001 and 2003, in the percentage of 16 - 17 year-olds in full-time education and full-time work?
Find 2001 on the 'year' axis and the corresponding percentage of pupils in full time work on the vertical axis. It is 22%.
Find the percentage of pupils in full-time education for the year 2001 on the vertical axis. It is 47%.
Repeat the process for the year 2003. The figures are 10% for full-time work and 64% for full-time education.
So the percentage of 16-17 year-olds moving into full-time work declined from 22% in 2001 to 10% in 2003, which is a fall of 12%.
The percentage in full-time education increased from 47% in 2001 to 64% in 2003, which is an increase of 17%.
Avoiding common errors
Most common errors can be avoided by:
- reading the title to check what the graph represents
- checking where the axes start
- checking which units are being used on each axis, and
- checking the scale on each axis.